WO2019131863A1 - Negative electrode material for lithium-ion secondary cells - Google Patents

Abstract

The present invention pertains to: a negative electrode material for lithium-ion secondary cells that includes a composite (A) comprising Si particles (A1) in which Al, Fe, Y, and Zr are each included in an amount of less than 10 μg per 1 g of the particles, particles (A2) comprising a graphite-containing substance, and a carbonaceous material (A3); a negative electrode sheet; and a lithium-ion secondary cell. This negative electrode substance makes it possible to obtain a lithium-ion secondary cell with a high delivered capacity deriving from Si particles by reducing, to the extent possible, impurities included in the Si particles.

Description

Negative electrode material for lithium ion secondary battery

The present invention relates to a negative electrode material for a lithium ion secondary battery.

The speed-up of the power saving of the electronic components has advanced the multifunctionalization of portable electronic devices, and the power consumption of the portable electronic devices is increasing. Therefore, there is a strong demand for higher capacity and smaller size of the lithium ion secondary battery, which is the main power source of portable electronic devices. In addition, demand for electric vehicles is increasing, and there is a strong demand for higher capacity in lithium ion secondary batteries used therein.

In order to meet such requirements, materials for negative electrodes in which silicon (Si) particles and a carbon material are combined have been proposed. However, a lithium ion secondary battery using a composite material of Si particles and a carbon material is greatly deteriorated due to a volume change at the time of charge and discharge peculiar to Si, although it has a high capacity. In order to cope with this, various measures such as forming of nano particles of Si, application of coating material to Si, doping of different metals to Si, etc. are taken, and cycle life is being improved while maintaining high capacity by these measures. .

However, if the Si particles contain impurities, the expression capacity of Si decreases, and the amount of Si necessary to express the same capacity increases. Even if the expansion of the Si particles is suppressed, the expansion of the negative electrode will increase if the amount of Si introduced to the negative electrode increases.

Therefore, several proposals have been made to remove impurities in Si particles. For example, Patent Document 1 contains Si, Al, Fe, and Zr, and the content of Si and Al is mass%, 60 ≦ Si + Al ≦ 80, 5 ≦ Al ≦ 50, mass ratio of Fe to Si [Fe ] / [Si] is 0.1 ≦ [Fe] / [Si] ≦ 0.33, and the mass ratio of Zr to Si [Zr] / [Si] is 0.1 ≦ [Zr] / [Si] ≦ A crystalline Si nucleus having a composition of 0.29, the balance being composed of one or more of Ni, Cr and Cu and unavoidable impurities, and further having an X-ray diffraction peak of the Si (111) plane. And a negative electrode active material for a lithium ion battery, the maximum diameter of which is less than 1 μm.

Unexamined-Japanese-Patent No. 2017-188271

Although Patent Document 1 refers to the amounts of Al, Fe, Zr, Ni, Cr, and Cu contained in Si particles, the method of reducing the content of elements other than Si as much as possible is not taken, and Si particles are used. It is insufficient to solve the problem of increased expression capacity derived from.
An object of the present invention is to provide a negative electrode material for obtaining a lithium ion secondary battery having a high capacity with a small content of Si particles.

The present invention includes the following aspects.
[1] Si particles (A1) and particles (A1) in which the average particle diameter d _AV of the primary particles is 5 nm or more and 95 nm or less, and Al, Fe, Y, and Zr contained in 1 g of particles are all less than 10 μg Lithium ion containing a composite (A) containing an amorphous carbon coating layer (A1C) having a thickness of 1 nm or more and 20 nm or less, particles (A2) made of a material containing graphite, and a carbonaceous material (A3) Negative electrode material for secondary battery.
[2] The particles (A2) have a 50% particle diameter _DV50 in the volume-based cumulative particle size distribution of 2.0 μm to 20.0 μm, and a BET specific surface area (S _BET ) of 1.0 m ² / g to 10 The negative electrode material for a lithium ion secondary battery as recited in the aforementioned Item 1, which has a particle size of not more than 0 m ² / g.
[3] In the particles (A2), the ratio I ₁₁₀ / I ₀₀₄ of the peak intensity I ₁₁₀ of the ( ₁₁₀ ) plane to the peak intensity I ₀₀₄ of the (004) plane by powder X-ray diffraction method is 0.10 or more 0.35 or less, the average interplanar spacing d ₀₀₂ of the (002) plane by powder X-ray diffraction is 0.3360 nm or less, and the total fineness of pores with a diameter of 0.4 μm or less measured by nitrogen gas adsorption The negative electrode material for a lithium ion secondary battery according to the above 1 or 2, which is a graphite particle having a pore volume of 5.0 μL / g to 40.0 μL / g.
[4] The negative electrode material for a lithium ion secondary battery according to any one of the aforementioned Items 1 to 3, wherein the content of the particles (A1) in the composite (A) is 10% by mass to 70% by mass. .
[5] A sheet-like current collector and a negative electrode layer for covering the current collector, the negative electrode layer comprising a binder, a conductive additive and the negative electrode for lithium ion secondary battery according to any one of the above 1 to 4 Material containing negative electrode sheet.
[6] A lithium ion secondary battery having the negative electrode sheet described in the preceding item 5.

A negative electrode material for a lithium ion secondary battery according to an embodiment of the present invention realizes a lithium ion secondary battery which has a high expression capacity derived from Si and can express a constant capacity with a smaller amount of Si contained. Can.

A negative electrode material for a lithium ion secondary battery according to an embodiment of the present invention is a composite (particles (A1), an amorphous carbon coating layer (A1C), particles (A2), and a carbonaceous material (A3) A) is included.

(1) Particle (A1)
The particles (A1) used in one embodiment of the present invention have Si as a main component capable of absorbing and desorbing lithium ions, and the content of Si is preferably 90% by mass or more, more preferably 95% by mass or more It is. The particles (A1) may be composed of a simple substance of Si or a compound containing a Si element, a mixture, a eutectic or a solid solution. In addition, the particles (A1) before being complexed with the particles (A2) and the carbonaceous material (A3) may be aggregations of a plurality of fine particles, that is, secondary particles. As a shape of particle | grains (A1), a lump shape, scale shape, spherical shape, fibrous shape etc. can be mentioned. Among these, spherical or massive is preferable.

As the substance containing Si element, Al, Fe, Y or Zr contained in 1 g of Si particles is preferably less than 100 μg, more preferably less than 10 μg. If 100 μg or more of any of Al, Fe, Y, or Zr contained in 1 g of Si particles is contained, the expression capacity is reduced.

The determination of Al, Fe, Y and Zr can be performed by ICP-AES analysis using, for example, Vista-Pro (Hitachi High-Tech Science; HF resistant torch, HF resistant chamber). Specifically, about 0.1 g of a sample is weighed in a PFA beaker, desulfurized nitric acid is decomposed to decompose carbon, and after cooling, the volume is adjusted to 50 ml and ICP-AES analysis is performed.

The lower limit of the average particle diameter d _AV of the primary particles of the particles (A1) is 5 nm, preferably 10 nm, and more preferably 35 nm. Further, the upper limit value of d _AV of the primary particles is 95 nm, preferably 70 nm. When the d _{AV of the} primary particles of the particles (A1) is larger than 95 nm, the particles (A1) expand and shrink in volume due to charge and discharge and the influence on the structure of the composite (A) containing the particles (A1) increases. Maintenance rate decreases. When the d _{AV of the} primary particles is smaller than 5 nm, the specific surface area of the particles (A1) is increased, and the amount of side reaction is increased.
Average particle diameter d _AV [nm] is
d _AV [nm] = 6 x 10 ³ / (ρ x S _BET )
Defined by Here, [[g / cm ³ ] is the true density of Si particles, and the theoretical value of 2.3 [g / cm ³ ] was adopted. S _BET [m ² / g] is a specific surface area measured by the BET method using N ₂ gas as an adsorption gas.

The particles (A1) are coated on their surface with a thin amorphous carbon coating layer (A1C). The upper limit of the thickness of the amorphous carbon coating layer (A1C) is 20 nm, preferably 10 nm, more preferably 5 nm. This is to suppress the side reaction between the electrolytic solution and the amorphous carbon coating layer (A1C). The lower limit of the thickness of the amorphous carbon coating layer (A1C) is 1 nm. This is because the oxidation of the particles (A1) and the aggregation of the particles (A1) are suppressed. In addition, since the particles (A1) in which side reactions with the electrolytic solution proceed more frequently than the amorphous carbon coating layer (A1C) are coated with the amorphous carbon coating layer (A1C), the initial coulombic efficiency is significantly increased. Improve. Further, by suppressing the side reaction, it is possible to suppress the consumption of the electrolytic solution such as fluoroethylene carbonate (FEC).

The thickness of the amorphous carbon coating layer (A1C) can be determined by measuring the film thickness in an image taken by observation with a transmission electron microscope (TEM). An example of a specific TEM observation is shown below.
Device: H9500 manufactured by Hitachi, Ltd.
Acceleration voltage: 300 kV.
Preparation of sample: A small amount of sample is taken in ethanol and dispersed by ultrasonic irradiation, and then placed on a microgrid observation mesh (without a supporting film) to make an observation sample.
Observation magnification: 50,000 times (at the time of particle shape observation) and 400,000 times (at the time of thickness observation of an amorphous carbon layer)

The core-shell structure (hereinafter referred to as a structure (α)) comprising particles (A1) and an amorphous carbon coating layer (A1C) covering the particles preferably has a BET specific surface area of 25 m ² / g to 70 m. ^{It is 2} / g or less, more preferably 52 m ² / g or more and 67 m ² / g or less. Moreover, the density of primary particles is 2.2 g / cm ³ or more. When the BET specific surface area (S _BET ) of the structure (α) is 25 m ² / g or more, the particle diameter of the structure (α) does not become too large, and the electron transfer path in the solid of the structure (α) and Li The ion diffusion path will not be long. That is, the resistance at the time of charge and discharge is kept low. Furthermore, the absolute value of the amount of expansion per particle of the structure (α) does not increase, and the possibility of destruction of the structure of the complex (A) around the structure (α) is low. In addition, when the density of the structure (α) is 2.2 g / cm ³ or more, it is also advantageous in terms of volumetric energy density.

The content of particles (A1) in the composite (A) is preferably 2% by mass to 95% by mass, more preferably 5% by mass to 80% by mass, and still more preferably 10% by mass to 70% by mass It is. When the content of particles (A1) is 95% by mass or less, the electrical resistance can be suppressed low. When the content of the particles (A1) is 2% by mass or more, the superiority in terms of volume or mass energy density is maintained.

The structure (α) composed of the particles (A1) and the amorphous carbon coating layer (A1C) can be produced by any of the solid phase method, liquid phase method and gas phase method, but the gas phase method is preferable. In particular, a method of producing Si particles from a vapor phase Si raw material such as monosilane by the CVD method, and thereafter producing a uniform amorphous carbon coating layer (A1C) by the CVD method using a carbon raw material such as acetylene or ethylene Is preferred.

(2) Particles (A2)
The graphite particles contained in the particles (A2) in the preferred embodiment of the present invention are preferably artificial graphite particles. The size and shape of the optical structure are in a specific range, and an artificial graphite particle having an appropriate degree of graphitization can provide an electrode material having both excellent crushing characteristics and battery characteristics.

In the present specification, D _V 50 represents a 50% particle size in a volume-based particle size distribution measured by a laser diffraction particle size distribution analyzer, and represents an apparent diameter of particles.

The 50% particle diameter D _V50 in the volume-based cumulative particle size distribution of the graphite particles contained in the particles (A2) in the preferred embodiment of the present invention is preferably 2.0 μm or more and 20.0 μm or less, more preferably 5.0 μm or more 18 .0 μm or less. If the D _{V 50} is 2.0 μm or more, it is not necessary to grind with a special device at the time of grinding, and energy can be saved. Moreover, since it is hard to cause aggregation, the handling property at the time of coating is also good. Furthermore, since the specific surface area does not become excessively large, the decrease in the initial charge and discharge efficiency does not occur. On the other hand, if D _{V 50} is 20.0 μm or less, it does not take time to diffuse lithium in the negative electrode material, and hence the input / output characteristics are good. Further, since silicon-containing particles are uniformly compounded on the surface of the graphite particles, good cycle characteristics can be obtained.

Graphite particles contained in the particle (A2) in a preferred embodiment of the present invention, BET specific surface area of preferably 1.0 m ² / g or more 10.0 m ² / g or less by N ₂ gas adsorption method, 3.0 m ² / g or more and 7.5 m ² / g or less is more preferable. When the BET specific surface area of the graphite particles is in the above range, a large area in contact with the electrolytic solution can be secured while suppressing an irreversible side reaction as a negative electrode material, so that the input / output characteristics are improved.

The artificial graphite particles contained in the particles (A2) in the preferred embodiment of the present invention have peak intensities I ₁₁₀ of the (110) plane of the graphite crystal and peaks of the (004) plane in the diffraction peak profile obtained by powder X-ray diffraction. it preferably has a specific I ₁₁₀ / I ₀₀₄ intensity I ₀₀₄ is 0.10 or more 0.35 or less. The ratio is more preferably 0.18 or more and 0.30 or less, and still more preferably 0.21 or more and 0.30 or less. If the ratio is 0.10 or more, the orientation is not too high, and the current collector surface of the electrode is due to expansion and contraction associated with insertion and desorption (occluding and releasing) of lithium ions to Si and graphite in the negative electrode material. There is no electrode expansion in the direction perpendicular to the above, and a good cycle life can be obtained. Further, since the carbon net plane of graphite is not parallel to the electrode plane, Li insertion is likely to occur, and good rapid charge / discharge characteristics can be obtained. If the ratio is 0.35 or less, the orientation is not too low, and the electrode density tends to increase when pressing is performed at the time of electrode preparation using the negative electrode material.

In the artificial graphite particles contained in the particles (A2) in a preferred embodiment of the present invention, the average interplanar spacing d ₀₀₂ of the (002) plane according to powder X-ray diffraction method is preferably 0.3360 nm or less. As a result, the amount of lithium insertion and desorption per mass of the artificial graphite particles in the negative electrode material itself is large, that is, the mass energy density also increases as the negative electrode material. In addition, expansion and contraction due to lithium insertion and removal from Si as a negative electrode material can be easily alleviated, and the cycle life is improved.
The thickness Lc in the C-axis direction of the crystallite of the artificial graphite particle is preferably 50 nm or more and 1000 nm or less from the viewpoint of mass energy density and crushability.

In the present specification, d ₀₀₂ and Lc can be measured by powder X-ray diffraction (XRD) according to a known method (Michio Inagaki, “carbon”, 1963, No. 36, pages 25-34; Iwashita et al., Carbon vol. 42 (2004), p. 701-714).

The artificial graphite particles contained in the particles (A2) in the preferred embodiment of the present invention have a total pore volume of 5.0 μL / g or more of pores with a diameter of 0.4 μm or less according to nitrogen gas adsorption BET method under liquid nitrogen cooling. It is preferably 40.0 μL / g or less. More preferably, it is 25.0 μL / g or more and 40.0 μL / g or less. An artificial graphite particle having a total pore volume of 5.0 μL / g or more tends to be complexed with the particle (A1) and the carbonaceous material (A3), and is preferable in terms of improvement of the cycle capacity retention rate. In a carbon material having Lc of 100 nm or more measured by X-ray diffraction method, when the total pore volume is 40.0 μL / g or less, a structure caused by anisotropic expansion and contraction of a graphite layer during charge and discharge Irreversible change is unlikely to occur, and the cycle characteristics of the negative electrode material are further improved. In addition, when the total pore volume of the artificial graphite particles is in this range, the electrolyte easily penetrates when the negative electrode material is used as an active material, which is preferable in view of rapid charge / discharge characteristics.

The artificial graphite particles contained in the particles (A2) in a preferred embodiment of the present invention have a peak intensity I _D of 1580 to 1620 cm of the peak derived from the amorphous component in the range of 1300 to 1400 cm.sup.- ¹ measured by Raman spectroscopy. The ratio I _D / I _G (R value) to the intensity I _G of the peak derived from the graphite component in the range of ^-1 is preferably 0.04 or more and 0.18 or less, preferably 0.08 or more and 0.16 or less It is further preferred that If the R value is 0.04 or more, the crystallinity of graphite is not too high, and good rapid charge / discharge characteristics can be obtained. If the R value is 0.18 or less, good cycle characteristics can be obtained without the occurrence of side reactions during charge and discharge due to the presence of defects.
The Raman spectrum can be measured, for example, by observing with a microscope attached using a laser Raman spectrophotometer (NRS-5100 manufactured by JASCO Corporation).

(3) Method of Producing Particles (A2) The graphite particles contained in the particles (A2) according to one embodiment of the present invention may be produced by heating particles obtained by crushing coke having a heat history of 1000 ° C. or less. it can.
As a raw material of coke, for example, petroleum pitch, coal pitch, coal pitch coke, petroleum coke and mixtures thereof can be used. That is, as the graphite particles contained in the particles (A2), it is preferable to use a material derived from petroleum-based coke and / or coal-based coke. Among these, those subjected to delayed coking under specific conditions are desirable.

The raw material to be passed through a delayed coker is a decanted oil from which the catalyst has been removed after fluid bed catalytic cracking has been performed on heavy fractions at the time of crude oil refining, coal tar extracted from bituminous coal, etc. And those obtained by sufficiently distilling the tar obtained by raising the temperature to 100 ° C. or higher. During the delayed coking process, it is preferable that the temperature of these liquids be raised to 450 ° C. or higher, 500 ° C. or higher, or even 510 ° C. or higher at least at the entrance of the drum. The carbon content increases and the yield improves. The pressure in the drum is preferably maintained at normal pressure or higher, more preferably 300 kPa or higher, and still more preferably 400 kPa or higher. This further increases the capacity as the negative electrode. As described above, by performing coking under more severe conditions than usual, the liquid can be reacted more and coke having a higher degree of polymerization can be obtained.

The obtained coke is cut out from the inside of the drum by a jet water flow, and the obtained mass is roughly crushed to about 5 cm with a gold crucible or the like. Although a twin-roll crusher or a jaw crusher can also be used for the coarse grinding, it is preferable that the 1 mm sieve is ground to have 90% by mass or more. By crushing as described above, it is possible to prevent inconveniences such as popping up of coke powder and increase in burnout after drying in the subsequent heating process and the like.

The coke is then crushed.
In the case of dry pulverization, if the coke contains water at the time of pulverization, the pulverization property is significantly reduced, so it is preferable to previously dry it at about 100 to 1000.degree. More preferably, it is 100 to 500 ° C. When the coke has a high heat history, the crushing strength becomes strong and the crushability deteriorates, and the crystal anisotropy develops, so that the cleavage property becomes strong and it becomes easy to be a scaly powder. There is no particular limitation on the method of pulverizing, and a known jet mill, hammer mill, roller mill, pin mill, vibration mill or the like can be used.
Milling is preferably carried out as D _V50 becomes 2.0μm or 20.0μm or less, and more preferably more than 5.0 .mu.m 18.0.

Graphitization is preferably performed at a temperature of 2400 ° C. or higher, more preferably 2800 ° C. or higher, still more preferably 3050 ° C. or higher, still more preferably 3150 ° C. or higher under an inert atmosphere (eg, nitrogen gas or argon gas atmosphere) Do. When treated at a higher temperature, more graphite crystals grow, and an electrode capable of storing lithium ions with higher capacity can be obtained. On the other hand, if the temperature is too high, it is difficult to prevent the sublimation of the graphite powder, and the energy required becomes too large. Therefore, the graphitization temperature is preferably 3600 ° C. or less.

It is preferred to use electrical energy to achieve these temperatures. Electrical energy is expensive compared to other heat sources and consumes a great deal of power, especially to achieve 2000 ° C. or higher. Therefore, it is preferable not to consume electrical energy other than graphitization. Prior to graphitization, it is preferable that the carbon raw material be calcined to remove organic volatile components, that is, the fixed carbon content is 95% or more, more preferably 98% or more, and still more preferably 99% or more. This firing can be performed, for example, by heating at 700 to 1500.degree. Since the reduction in mass at the time of graphitization is reduced by firing, the throughput of the graphitization processing apparatus can be increased once.

After graphitization, it is preferable not to carry out the pulverizing treatment. However, it can be crushed to such an extent that the particles are not crushed after graphitization.
When an electrode is produced using graphite particles as an active material, the active material is easily distributed uniformly inside the electrode at the time of electrode compression, and the contact with adjacent particles is also stable, and thus a battery having more excellent charge and discharge repeatedly. can do.

(4) Carbonaceous material (A3)
The carbonaceous material (A3) in a preferred embodiment of the present invention is a carbon material which is different from the particles (A2) and in which the development of crystals formed by carbon atoms is low, and a Raman spectrum by Raman scattering spectroscopy. Has a peak near 1360 cm ^-1 . The carbonaceous material (A3) may be the same as the amorphous carbon coating layer (A1C).
The carbonaceous material (A3) can be produced, for example, by carbonizing a carbon precursor. The carbon precursor is not particularly limited, but includes, but not limited to, thermal heavy oil, pyrolysis oil, straight asphalt, blown asphalt, petroleum-derived substances such as tar or petroleum pitch by-produced during ethylene production, coal tar produced during coal distillation, The heavy component obtained by distilling off the low-boiling component of coal tar, and coal-derived materials such as coal tar pitch (coal pitch) are preferred, and petroleum pitch or coal pitch is particularly preferred. Pitch is a mixture of multiple polycyclic aromatic compounds. When pitch is used, a carbonaceous material (A3) with few impurities can be produced at a high carbonization rate. Since the pitch has a low oxygen content, when the particles (A1) are coated with the carbonaceous material, the particles (A1) are less likely to be oxidized.

The pitch as a precursor of the carbonaceous material (A3) preferably has a softening point of 80 ° C. or more and 300 ° C. or less. If the softening point of pitch is 80 ° C. or higher, the average molecular weight of the polycyclic aromatic compound constituting it is not too small, and the volatile content is also relatively small, so the carbonization rate decreases, the manufacturing cost increases, and further There is no problem that a carbonaceous material (A3) having a large specific surface area containing many pores can be easily obtained. If the softening point of the pitch is 300 ° C. or less, the viscosity is not too high, so that it can be uniformly mixed with the particles (A1). The softening point of pitch can be measured by the Mettler method described in ASTM-D 3104-77.

The pitch of the carbonaceous material (A3) as a precursor is preferably 20% by mass to 70% by mass, and more preferably 25% by mass to 60% by mass, as a residual carbon ratio. When the residual carbon ratio of the pitch is 20% by mass or more, problems such as an increase in manufacturing cost and a carbonaceous material having a large specific surface area do not occur. If the residual carbon ratio of the pitch is 70% by mass or less, the viscosity is not too high, and therefore, it can be uniformly mixed with the particles (A1).
The residual coal rate is determined by the following method. The solid pitch is ground in a mortar or the like, and the ground product is subjected to mass thermal analysis under a nitrogen gas flow. The ratio of mass to charged mass at 1100 ° C. is defined as the residual carbon ratio.

The pitch used in the present invention preferably has a QI (quinoline insoluble content) content of 10% by mass or less, more preferably 5% by mass or less, and still more preferably 2% by mass or less. The QI content of pitch is a value corresponding to the amount of free carbon. When the pitch containing a large amount of free carbon is heat-treated, the free carbon adheres to the surface of the sphere to form a three-dimensional network in the process of appearance of mesophase spheres, thereby hindering the growth of the sphere, and thus it tends to be a mosaic structure. On the other hand, when heat treatment is performed on a pitch having a small amount of free carbon, mesophase spheres grow large and tend to generate needle coke. When the QI content is in the above range, the electrode characteristics are further improved.

The pitch used in the present invention preferably has a TI (toluene insoluble content) content of 10% by mass to 70% by mass. The pitch with low TI content has a low average carbon weight and high volatile content because the polycyclic aromatic compound constituting it has a low carbonization rate, an increase in production cost, and a large specific surface area including many pores. Carbonaceous materials are easily obtained. The pitch with a high TI content has a high carbonization rate because the average molecular weight of the polycyclic aromatic compound constituting it is high, but the pitch with a high TI content is uniformly mixed with the particles (A1) since the viscosity is high. It tends to be difficult. When the TI content is in the above-mentioned range, it is possible to uniformly mix the pitch and the other components, and to obtain a negative electrode material having characteristics suitable as a battery active material.

The QI content and the TI content of the pitch used in the present invention can be measured by the method described in JIS K2425 or a method according thereto.

The mass ratio of the carbonaceous material (A3) to the total mass of the particles (A1), the particles (A2) and the carbonaceous material (A3) is preferably 2% by mass to 40% by mass, and more preferably 4% % Or more and 30% by mass or less.
When the proportion of the carbonaceous material (A3) is 2% by mass or more, sufficient bonding between the particles (A1) and the particles (A2) can be obtained, and the surface of the particles (A1) can be a carbonaceous material (A3) As it becomes possible to cover, conductivity is easily imparted to the particles (A1), and an effect of suppressing surface reactivity of the particles (A1) and an effect of alleviating expansion and contraction are obtained, and good cycle characteristics are obtained. Be On the other hand, if the proportion of the carbonaceous material (A3) is 40% by mass or less, the initial efficiency does not decrease even if the proportion of the carbonaceous material (A3) is high.

(5) Complex (A)
The composite (A) according to one embodiment of the present invention comprises a structure (α) comprising particles (A1) and an amorphous carbon coating layer (A1C), particles (A2), and a carbonaceous material (A3). It is preferable that at least a part of the structure (α), the particles (A2) and the carbonaceous material (A3) be complexed with each other. The complexing is, for example, a state in which the structure (α) and the particle (A2) are fixed by the carbonaceous material (A3) and bound, or the structure (α) and / or the particle (A2) is carbon The state covered with the quality material (A3) can be mentioned. In the present invention, it is preferable that the structure (α) is completely covered with the carbonaceous material (A3) and the surface of the structure (α) is not exposed, among which the structure (α) And particles (A2) are linked via the carbonaceous material (A3), and the whole is covered with the carbonaceous material (A3), and the structure (α) and particles (A2) are in direct contact It is preferable that the whole is covered with the carbonaceous material (A3).
When used as a negative electrode material in a battery, the surface of the structure (α) is not exposed, so that the electrolytic solution decomposition reaction is suppressed and the coulombic efficiency can be maintained high, and particles (the carbonaceous material (A3) A2) and the structure (α) can increase the conductivity between each other, and the structure (α) is covered with the carbonaceous material (A3) to be accompanied by its expansion and contraction. Volume changes can be buffered.

The composite (A) according to an embodiment of the present invention may contain the particles (A2), the carbonaceous material (A3) or the structure (α) alone, which are not complexed. It is preferable that the amount of the particles (A2), the carbonaceous material (A3), or the structures (α) contained alone without being complexed is small, and specifically, to the mass of the complex (A) On the other hand, it is preferably 10% by mass or less.

As for DV50 of the complex (A) which _concerns on one Embodiment of this invention, 2.0 micrometers or more and 20.0 micrometers or less are preferable. More preferably, it is 2.0 micrometers or more and 18.0 micrometers or less. If _DV50 is 2.0 micrometers or more, economical manufacture is possible. Also, there is no difficulty in increasing the electrode density. Furthermore, since the specific surface area is not excessively increased, the decrease in the initial charge and discharge efficiency due to the side reaction with the electrolytic solution does not occur. Further, if the _DV50 is 20.0 μm or less, good input / output characteristics and cycle characteristics can be obtained.

The BET specific surface area of the composite (A) according to one embodiment of the present invention is preferably 1.0 m ² / g or more and 10.0 m ² / g or less. More preferably, it is 1.0 m ² / g or more and 5.0 m ² / g or less. If the BET specific surface area (S _BET ) is 1.0 m ² / g or more, uniform distribution in the electrode is maintained without deterioration of input / output characteristics, and good cycle characteristics can be obtained. When the BET specific surface area (S _BET ) is 10.0 m ² / g or less, the coating property is not lowered and the handling property is also good. In addition, it is easy to increase the electrode density without requiring a large amount of binder for electrode production, and it is possible to suppress the decrease in the initial charge and discharge efficiency due to the side reaction with the electrolytic solution.

The complex (A) according to one embodiment of the present invention has a peak intensity I _D of a peak in the range of 1300 to 1400 cm ⁻¹ in a Raman spectrum obtained by measuring the particle end face with a microscopic Raman spectrometer. And the ratio I _D / I _G (R value) of the peak intensity to the peak intensity I _{G in} the range of 1580 to 1620 cm ^-1 is preferably 0.15 or more and 1.0 or less. More preferably, it is 0.2 or more and 1.0 or less, still more preferably 0.4 or more and 1.0 or less. The fact that the R value is too small means that the surface of the particles (A2) is exposed to a certain amount. Therefore, if the R value is 0.15 or more, the particles (A2) and the particles (A1) are covered with the carbonaceous material (A3), and the effect of suppressing the surface reactivity of the particles (A1) or expansion and contraction Good cycle characteristics can be obtained because the effect of relieving is increased. On the other hand, when the R value is too large, it indicates that the carbonaceous material (A3) containing a large amount of amorphous carbon having a large initial irreversible capacity covers the surface of the particles (A2). Therefore, if R value is 1.0 or less, the fall of initial stage discharge efficiency is suppressed.

(6) Method of Producing Complex (A) The complex (A) according to an embodiment of the present invention can be produced according to a known method.
For example, the structure (α) consisting of the particles (A1) and the amorphous carbon coating layer (A1C), the particles (A2) and the precursor of the carbonaceous material (A3) are mixed, and the obtained mixture is heat-treated Complex (A) can be obtained by the method including making the said precursor into carbonaceous material (A3).
The mixture of the structure (α), the particles (A2) and the precursor of the carbonaceous material (A3), for example, melts the pitch which is one of the precursors of the carbonaceous material (A3), and the molten pitch and structure By mixing the body (α) in an inert atmosphere, solidifying and then grinding the mixture, and mixing the ground product with the particles (A2); the structure (α) and the particles (A2) By mixing and then mixing the mixture of the structure (α) and the particles (A2) with the carbonaceous material (A3) precursor and performing the mechanochemical treatment; or the carbonaceous material (A3) precursor in the solvent It can be obtained by dissolving, adding and mixing the structure (α) and the particles (A2) to the precursor solution, removing the solvent and grinding the solid obtained. For the mechanochemical treatment, for example, a known device such as a hybridizer (registered trademark, manufactured by Nara Machinery Co., Ltd.) can be used.

For grinding and mixing, known devices and apparatus such as ball mill, jet mill, rod mill, pin mill, rotary cutter mill, hammer mill, atomizer, mortar and the like can be used, but the particles (A1) and the structure (α) It is preferable to adopt a method that does not increase the degree of oxidation of In general, it is considered that oxidation tends to progress to small particle size particles having a large specific surface area, so grinding of large particle size particles preferentially proceeds, and apparatus in which small particle size particles do not progress much is preferable. For example, in means for mainly crushing by impact, such as a rod mill, a hammer mill, etc., the impact force tends to be transmitted preferentially to large particle size particles and not to much to small particle size particles. The means of grinding mainly by impact and shear, such as a pin mill and a rotary cutter mill, tends to transmit shear force preferentially to large particle size particles and less to small particle size particles. Such an apparatus can be used to grind or mix the particles (A1) and the structure (α) without promoting oxidation.

Further, in order to suppress the progress of oxidation of the particles (A1) and the structural body (α), it is preferable to carry out the aforementioned pulverization / mixing in a non-oxidative atmosphere. As the non-oxidizing atmosphere, an atmosphere filled with an inert gas such as argon gas or nitrogen gas can be mentioned.

The heat treatment for converting the carbonaceous material (A3) precursor to the carbonaceous material (A3) is preferably 200 ° C. or more and 2000 ° C. or less, more preferably 500 ° C. or more and 1500 ° C. or less, particularly preferably 600 ° C. or more and 1200 ° C. or less At a temperature of By this heat treatment, the carbonaceous material (A3) coats the structural body (α) and / or the particles (A2), and the carbonaceous material (A3) is between the structural bodies (α) and the particles (A2) And between the structure (α) and the particles (A2) to connect them. If the heat treatment temperature is too low, carbonization of the carbonaceous material (A3) precursor is not completed sufficiently, and hydrogen and oxygen may remain in the negative electrode material, which may adversely affect battery characteristics. On the other hand, if the heat treatment temperature is too high, crystallization proceeds too much to deteriorate the charge characteristics, or the constituent element of the particles (A1) and carbon may be combined to cause an inactive state with respect to Li ions. The heat treatment is preferably performed in a non-oxidative atmosphere. As the non-oxidizing atmosphere, an atmosphere filled with an inert gas such as argon gas or nitrogen gas can be mentioned. In addition, since the particles may be fused and agglomerated by heat treatment, it is preferable to crush the heat-treated product in order to use it as an electrode active material. As a crushing method, a pulperizer using an impact force such as a hammer, a jet mill using a collision of objects to be crushed and the like are preferable.

(7) Adjustment of capacity As a negative electrode material for lithium ion secondary batteries, a material containing composite (A) and carbon for the purpose of improving battery performance and adjusting the capacity of negative electrode materials for lithium ion secondary batteries It may be mixed. A plurality of types of materials containing carbon to be mixed may be used. As a material containing carbon, graphite having a high capacity is preferable. The graphite can be selected from natural graphite and artificial graphite. At this time, it is preferable to use a composite having a relatively high capacity (700 mAh / g or more) as the composite (A) because the cost of the negative electrode material for a lithium ion secondary battery can be reduced. The material containing carbon for adjusting the volume may be mixed with the composite (A) in advance, and additives such as a binder, a solvent, and a conductive additive may be added thereto to prepare a negative electrode paste. In addition, the negative electrode paste may be prepared by simultaneously mixing the composite (A), a material containing carbon, a binder, a solvent, an additive such as a solvent, a conductive additive, and the like. The order and method of mixing may be appropriately determined in consideration of powder handling and the like.

(8) Paste for Anode The paste for an anode according to one embodiment of the present invention contains the above-mentioned anode material, a binder, a solvent, and, if necessary, an additive such as a conductive aid. This negative electrode paste can be obtained, for example, by kneading the negative electrode material, the binder, the solvent, and the conductive auxiliary agent as needed. The negative electrode paste can be formed into a sheet, a pellet, or the like.

Examples of the material used as the binder include polyethylene, polypropylene, ethylene propylene terpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, acrylic rubber, and a polymer compound having a large ion conductivity. Examples of the polymer compound having large ion conductivity include polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphasphazen, polyacrylonitrile and the like. The amount of the binder is preferably 0.5 parts by mass to 100 parts by mass with respect to 100 parts by mass of the negative electrode material.

The conductive aid is not particularly limited as long as it plays the role of imparting conductivity and electrode stability (buffering action against volume change in insertion and detachment of lithium ions) to the electrode. For example, carbon nanotubes, carbon nanofibers, vapor-grown carbon fibers (for example, "VGCF (registered trademark)" manufactured by Showa Denko KK), conductive carbon (for example, "Denka Black (registered trademark)" Electric Chemical Industry Co., Ltd. Manufactured by "Super C65", manufactured by TIMCAL, "Super C45", manufactured by TIMCAL, manufactured by "KS6L", manufactured by TIMCAL, and the like. The amount of the conductive additive is preferably 10 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the negative electrode material.

The solvent is not particularly limited, and N-methyl-2-pyrrolidone, dimethylformamide, isopropanol, water and the like can be used. In the case of the binder which uses water as a solvent, it is preferable to use a thickener together. The amount of the solvent may be adjusted to have a viscosity such that the paste can be easily applied to the current collector.

(9) Negative electrode sheet The negative electrode sheet which concerns on one Embodiment of this invention has a collector and the electrode layer which coat | covers a collector.
As a collector, sheet-like things, such as nickel foil, copper foil, nickel mesh, or a copper mesh, are mentioned, for example.

The electrode layer contains a binder and the above-mentioned negative electrode material. The electrode layer can be obtained, for example, by applying the above-mentioned paste on a current collector and drying it. The application method of the paste is not particularly limited. The thickness of the electrode layer is preferably 50 to 200 μm. If the electrode layer is too thick, it may not be possible to accommodate the negative electrode sheet in a standardized battery container. The thickness of the electrode layer can be adjusted by the amount of paste applied. Moreover, after drying a paste, it can also adjust by pressure-molding. Examples of pressure molding methods include molding methods such as roll pressure and press pressure. The pressure for press molding is preferably about 100 to 500 MPa.

The electrode density of the negative electrode sheet can be calculated as follows. That is, the negative electrode sheet after pressing is punched into a circular shape having a diameter of 16 mm, and its mass and thickness are measured. The mass and thickness of the current collector foil (punched into a circular shape of 16 mm in diameter) separately measured therefrom are subtracted to obtain the mass and thickness of the electrode layer, and the electrode density is calculated based on the values.

(10) Lithium Ion Secondary Battery A lithium ion secondary battery according to an embodiment of the present invention comprises at least one selected from the group consisting of a non-aqueous electrolytic solution and a non-aqueous polymer electrolyte, a positive electrode sheet and the negative electrode sheet. Have.
As the positive electrode sheet, a sheet conventionally used in lithium ion secondary batteries, specifically, a sheet containing a positive electrode active material can be used. Examples of the positive electrode active material include LiNiO ₂ , LiCoO ₂ , LiMn ₂ O ₄ , LiNi _0.34 Mn _0.33 Co _0.33 O ₂ , LiFePO _{4 and the} like.

The non-aqueous electrolytic solution and the non-aqueous polymer electrolyte used for the lithium ion secondary battery are not particularly limited. For example, lithium carbonates such as LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene Organic electrolytes dissolved in non-aqueous solvents such as carbonate, butylene carbonate, acetonitrile, propionitrile, dimethoxyethane, tetrahydrofuran, γ-butyrolactone, etc. containing polyethylene oxide, polyacrylonitrile, polyfluorinated bilinidene, polymethyl methacrylate and the like Examples thereof include solid polymer electrolytes containing gel-like polymer electrolytes, polymers having ethylene oxide bonds, and the like.

In addition, a small amount of a substance that causes a decomposition reaction when charging a lithium ion secondary battery may be added to the electrolytic solution. Examples of the substance include vinylene carbonate (VC), biphenyl, propane sultone (PS), fluoroethylene carbonate (FEC), ethylene sultone (ES) and the like. As addition amount, 0.01 mass% or more and 50 mass% or less are preferable.

The lithium ion secondary battery can be provided with a separator between the positive electrode sheet and the negative electrode sheet. As the separator, for example, non-woven fabric mainly made of polyolefin such as polyethylene and polypropylene, cloth, microporous film, or a combination thereof can be mentioned.

Lithium-ion secondary batteries are used to power electronic devices such as mobile phones, personal computers and personal digital assistants; power sources for electric drills, electric vacuum cleaners and electric motors such as electric cars; fuel cells, solar power, wind power, etc. It can be used for storage of stored power.

Hereinafter, the present invention will be described in more detail by way of Examples and Comparative Examples. Note that these are merely illustrative for the purpose of illustration, and the present invention is in no way limited thereto. In Examples and Comparative Examples, the average particle diameter d _AV of the primary particles of the particles (A1), the thickness of the amorphous carbon coating layer (A1C), and the (002) plane of the artificial graphite particles by X-ray diffraction method The average interplanar spacing d _002, the thickness L _c in the C-axis direction of the crystallite, and the R value in the Raman spectrum are measured by the methods described in the “Embodiments of the Invention” herein. Moreover, the measurement of other physical properties and battery evaluation were performed as follows.

[Measurement of I ₁₁₀ / I ₀₀₄ by powder X-ray diffraction method]
A carbon powder sample was filled in a glass sample plate (sample plate window 18 × 20 mm, depth 0.2 mm), and measurement was performed under the following conditions.
X-ray diffractometer: Rigaku SmartLab (registered trademark),
X-ray type: Cu-Kα ray,
K beta radiation removal method: Ni filter,
X-ray output: 45 kV, 200 mA,
Measurement range: 5.0 to 10.0 deg,
Scanning speed: 10.0 deg. / Min.
The obtained waveform was subjected to smoothing, background removal, Kα2 removal, and profile fitting. The resulting (004) intensity ratio becomes orientation index from the peak intensity I ₁₁₀ between the peak intensity I ₀₀₄ (110) plane of the surface was calculated I ₁₁₀ / I _004. In addition, the peak of each surface selected the thing of the largest intensity among the following ranges as each peak.
(004) plane: 54.0 to 55.0 deg,
(110) plane: 76.5 to 78.0 deg.

[Particle diameter D _V50 ]
The powder was added to 2 cups of very small spatula and 2 drops of nonionic surfactant (TRITON®-X; manufactured by Roche Applied Science) in 50 ml of water and ultrasonically dispersed for 3 minutes. The dispersion was charged into a laser diffraction particle size distribution analyzer (LMS-2000e, manufactured by Seishin Enterprise Co., Ltd.), and the volume-based cumulative particle size distribution was measured to determine 50% particle diameter Dv ₅₀ (μm).

[Specific surface area]
Specific surface area / pore distribution measurement device (Quantam Chrome Instruments, NOVA 4200e), using nitrogen gas as a probe, BET specific surface area according to BET multipoint method with relative pressure of 0.1, 0.2, and 0.3 S _BET (m ² / g) was measured.

[Pore volume]
About 5 g of a carbon material was weighed in a glass cell and dried at 300 ° C. under a reduced pressure of 1 kPa or less for about 3 hours to remove adsorption components such as water, and then the mass of the carbon material was measured. Thereafter, the adsorption isotherm of nitrogen gas of the carbon material after drying under liquid nitrogen cooling was measured by Autosorb-1 manufactured by Quantachrome. The nitrogen adsorption amount at the measurement point of P / P ₀ = 0.992 to 0.995 of the obtained adsorption isotherm and the mass of the carbon material after drying, the total pore volume (μL / g) having a diameter of 0.4 μm or less Asked for).

[Production of negative electrode sheet]
As a binder, carboxymethylcellulose (CMC; manufactured by Daicel Corporation, CMC1300) was used. Specifically, an aqueous solution in which CMC powder having a solid content ratio of 2% was dissolved was obtained.
Prepare carbon black, carbon nanotubes (CNT), and vapor grown carbon fiber (VGCF (registered trademark) -H, Showa Denko KK) as a conductive additive, and each is 3: 1: 1 (mass ratio) The mixture was used as a mixed conductive aid.
90 parts by mass of a mixture of composite (A) manufactured in the following Examples and Comparative Examples and graphite as a material containing carbon for the purpose of adjusting volume, 2 parts by mass of mixed conductive aid, 8 parts by weight of solid CMC The CMC aqueous solution was mixed to be a part, and the mixture was kneaded by a rotation / revolution mixer to obtain a paste for a negative electrode.
Alternatively, 90 parts by mass of the composite (A) manufactured in Examples and Comparative Examples, 2 parts by mass of mixed conductive support agent, and CMC aqueous solution are mixed so that the solid content of CMC is 8 parts by mass, using a rotation / revolution mixer It knead | mixed and obtained the paste for negative electrodes.
The negative electrode paste was uniformly coated on a copper foil with a thickness of 20 μm using a doctor blade with a gap of 300 μm, dried on a hot plate, and then vacuum dried to obtain a negative electrode sheet. The dried electrode was pressed by a uniaxial press at a pressure of 300 MPa to obtain a negative electrode sheet for battery evaluation.

[Fabrication of evaluation battery]
The following operation was carried out in a glove box maintained in a dry argon gas atmosphere with a dew point of −80 ° C. or less.

[Tripolar laminated half cell]
A negative electrode piece with an area of 4 cm ² (with a Cu foil tab) punched out of the above-mentioned negative electrode sheet, and an Li piece for counter electrode with an area of 7.5 cm ² (3.0 cm × 2.5 cm) cut out with a Li roll, and an area of 3.75 cm ² (1.5 cm x 2.5 cm) Li pieces for reference electrodes were obtained. A 5 mm wide Ni tab for a counter electrode and a reference electrode was prepared, and a 5 mm × 20 mm Ni mesh was attached so as to overlap with the tip 5 mm portion. Under the present circumstances, 5 mm width of Ni tab and 5 mm width of Ni mesh were made to correspond. The Cu foil tab of the above negative electrode piece was attached to the Ni tab of the working electrode. The Ni mesh at the tip of the Ni tab for the counter electrode was attached to the corner of the Li piece so as to be perpendicular to the 3.0 cm side of the Li piece for the counter electrode. The Ni mesh at the tip of the Ni tab for the reference electrode was attached to the center of the 1.5 cm side of the Li piece so as to be perpendicular to the 1.5 cm side of the Li piece for the reference electrode. A polypropylene film microporous membrane is sandwiched between the working electrode and the counter electrode, and the reference electrode is liquid-wound near the working electrode and through the polypropylene film microporous membrane so as to prevent a short circuit. It packed and the electrolyte solution was poured. Thereafter, the opening was sealed by heat fusion to prepare a battery for evaluation. The electrolyte solution is 1% by mass of vinylene carbonate (VC) in a solvent in which ethylene carbonate, ethyl methyl carbonate and diethyl carbonate are mixed in a volume ratio of 3: 5: 2, as in the bipolar laminate type full cell, It is a liquid obtained by mixing 10% by mass of fluoroethylene carbonate (FEC) and further dissolving the electrolyte LiPF ₆ so as to have a concentration of 1 mol / L.

[Definition of charge and discharge]
Charging refers to applying a voltage to the cell, and discharging refers to an operation that consumes the voltage of the cell.
In the case of a tripolar laminate type half cell, the counter electrode is Li metal, and the above negative electrode sheet is treated substantially as a positive electrode. Therefore, charging in the three-electrode laminate type half cell is an operation of releasing Li from the negative electrode sheet. On the other hand, the discharge of the tripolar laminate type half cell is an operation of inserting Li into the negative electrode sheet.

[Initial removal capacity]
The test was performed using a tripolar laminate type half cell. From rest potential 0.005 V vs. CC (constant current: constant current) discharge was performed at a current value of 0.1 C until Li / Li ⁺ . Next, 0.005 V vs. It switched to CV (constant volt | bolt: constant voltage) discharge with Li / Li ^<+ >, and performed discharge with the cut-off current value 0.005C.
Upper limit potential 1.5 V vs. Charging was performed at a current value of 0.1 C in CC mode as Li / Li ⁺ .
The test was performed in a thermostat set at 25 ° C. At this time, the capacity at the time of Li release from the working electrode for the first time was taken as the initial de-Li capacity.

The materials used in the following examples and comparative examples are as follows.
(1) Silicon-containing particles (Si fine particles)
Physical properties of Si particles and Si (1) to Si (2) used for the particles (A1) in Examples and Comparative Examples are shown in Table 1.
The average particle diameter d _AV of the primary particles is d _AV [nm] = 6 × 10 ³ / (ρ × S _BET ) as described above. Here, ρ is the true density (2.3 [g / cm ³ as theoretical value) of Si particles, and S _BET is the specific surface area [m ² / g] measured by the BET method.

Determination of Al, Fe, Y and Zr in each Si particle was carried out by ICP-AES analysis using Vista-Pro (Hitachi High-Tech Science; HF-resistant torch, HF-resistant chamber). Specifically, about 0.1 g of a sample was weighed in a PFA beaker and subjected to sulfuric acid decomposition to decompose carbon. After cooling, the volume was adjusted to 50 ml and ICP-AES analysis was performed.

(2) Preparation of structure (α) After preparing Si fine particle Si (1) by the CVD method, the structure is continuously formed by forming a carbon coating layer with a thickness of 2 nm by the CVD method using acetylene gas as a raw material α) -1 was obtained (Table 1). The structure (α) was not produced for the Si fine particles Si (2).

(3) Pitch Petroleum pitch (softening point 220 ° C.) was used. It was 52 mass% when the residual carbon rate in 1100 degreeC was measured by thermal analysis under nitrogen gas distribution about this petroleum pitch.
Further, the QI content of the petroleum pitch measured by the method described in JIS K2425 or a method according to the same was 0.62% by mass, and the TI content was 48.9% by mass.

(4) Graphite particles The physical properties of graphite particles used as a material containing carbon for the purpose of adjusting the volume together with the particles (A2) in Examples and Comparative Examples are shown in Table 2.

Example 1:
After petroleum-based coke is crushed by a bantam mill (manufactured by Hosokawa Micron Corporation), it is further crushed by a jet mill (manufactured by Seishin Enterprise Co., Ltd.) and heat-treated at 3000 ° C. in an Achison furnace to give a D _{V 50} of 7.5 μm. Artificial graphite particles (A2) -a having a BET specific surface area of 4.9 m ² / g were obtained.
Next, 16.4 parts by mass of the structure (α) -1 and 15.4 parts by mass of the petroleum pitch (as a mass after carbonizing the petroleum pitch), which is a precursor of the carbonaceous material (A3), are separated. It was charged into a bull flask. Nitrogen gas was circulated to maintain an inert atmosphere, and the temperature was raised to 250 ° C. The mixer was rotated at 500 rpm for agitation to uniformly mix the pitch and the silicon-containing particles. It was cooled and solidified to obtain a mixture.
68.2 parts by mass of the above-mentioned artificial graphite particles which are particles (A2) -a are added to this mixture, charged into a rotary cutter mill, and mixed at a high speed of 25000 rpm and mixed while maintaining an inert atmosphere by flowing nitrogen gas. I did.
This was placed in a baking furnace, raised to 1100 ° C. at 150 ° C./h under nitrogen gas flow, and held at 1100 ° C. for 1 hour to convert the (A3) precursor into (A3). The mixture was cooled to room temperature, taken out from a calcining furnace, crushed with a rotary cutter mill, and sieved with a 45 μm mesh sieve to obtain a sieved part as a composite (A) -a. Incidentally, Si (1) in the complex (A) -a is adjusted to be 10% by mass.

Apart from the above, pulverized petroleum coke in a bantam mill (manufactured by Hosokawa Micron Corporation), which was heat-treated at 3000 ° C. in an Acheson furnace, D _V50 is 12.1Myuemu, BET specific surface area of 2.5 m ² / g Graphite (1) was obtained. Further, after pulverizing the petroleum coke with a bantam mill (manufactured by Hosokawa Micron Corporation), and further pulverized with a jet mill (Seishin Ltd. company), which was heat-treated at 3000 ° C. the at Acheson furnace, D _V50 is 6. Graphite (2) having a BET specific surface area of 6.1 m ² / g at 7 μm was obtained.

A negative electrode using a mixture of composite (A) -a alone and 67.0 parts by mass of composite (A) -a, 16.5 parts by mass of graphite (1) and 16.5 parts by mass of graphite (2) Sheets were prepared and battery characteristics were measured. The results are shown in Table 3.

Comparative Example 1:
A complex (A) -b was obtained in the same manner as in Example 1 except that the structure (α) -1 was changed to Si (2) in Table 1.

Negative electrode sheet using a mixture of composite (A) -b alone and 67.0 parts by mass of composite (A) -b, 16.5 parts by mass of graphite (1) and 16.5 parts by mass of graphite (2) Were prepared and the battery characteristics were measured. The results are shown in Table 3.

In the results shown in Table 3, when Example 1 and Comparative Example 1 are compared, the contents of Al, Fe, Y and Zr contained in 1 g of Si particles are all 10 μm or less of the measurement limit in Example 1. Thus, the capacity to express 1 g of particles (A1) is increased. In fact, the initial volume of Example 1 containing 10% by mass of the particles (A1) is significantly increased as compared to Comparative Example 1.

Claims (6)

1. Thickness that covers Si particles (A1) and particles (A1) in which average particle diameter d _AV of primary particles is 5 nm or more and 95 nm or less, and Al, Fe, Y, and Zr contained in 1 g of particles are all less than 10 μg Negative electrode material for lithium ion secondary battery, including composite (A) including composite (A) containing particles (A2) of amorphous carbon coating layer (A1C) of 1 nm to 20 nm and particles containing graphite, and carbonaceous material (A3) .
2. The particles (A2) have a 50% particle diameter _DV50 in the volume-based cumulative particle size distribution of 2.0 μm to 20.0 μm, and a BET specific surface area (S _BET ) of 1.0 m ² / g to 10.0 m ² The negative electrode material for a lithium ion secondary battery according to claim 1, which is not more than 1 / g.
3. In the particles (A2), the ratio I ₁₁₀ / I ₀₀₄ of the peak intensity I ₁₁₀ of the ( ₁₁₀ ) plane to the peak intensity I ₀₀₄ of the (004) plane by powder X-ray diffraction method is 0.10 or more and 0.35 Or less, the average interplanar spacing d ₀₀₂ of the (002) plane by powder X-ray diffraction is 0.3360 nm or less, and the total pore volume of pores with a diameter of 0.4 μm or less measured by nitrogen gas adsorption is The negative electrode material for a lithium ion secondary battery according to claim 1 or 2, which is a graphite particle of 5.0 μL / g or more and 40.0 μL / g or less.
4. The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein a content of the particles (A1) in the composite (A) is 10% by mass to 70% by mass.
5. A sheet-like current collector and a negative electrode layer for covering the current collector, the negative electrode layer comprising a binder, a conductive additive and a negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 4. Negative electrode sheet.
6. A lithium ion secondary battery comprising the negative electrode sheet according to claim 5.